1. Field of Art
The present invention relates to a thermal control coating composition which is coated on the surface of an antenna or tower used in an artificial satellite or space station to control the incomings and outgoings of heat thereby to maintain the temperature of such a member (antenna or tower) within a range of operation temperature.
2. Prior Art Statement
Instruments used in an artificial satellite or like system are generally exposed to severe environment, and hence they must withstand severe environmental conditions to have high reliability, and yet they must be light in weight. For example, an antenna of an artificial satellite is subjected to severe temperature difference, since it is exposed directly to the solar lights at some time and it is cooled to an extremely low temperature when it is held in the shade. In order to ensure proper operation of the antenna, the temperature of the antenna must be maintained below about 100.degree. C. Since the temperature of the antenna is determined by the balance between the thermal energy of the absorbed solar light and the emitted thermal energy due to the radiation from the antenna, it becomes necessary to increase the radiation heat emitted from the antenna when the temperature thereof is raised or to descrease absorption of solar energy by the antenna.
In order to maintain the temperature of an antenna of an artificial satellite below 100.degree. C., a thermal control coating has hitherto been used to decrease the absorption of solar energy incident to the antenna and to emit the thermal energy to the aerospace. The properties of such a thermal control coating are determined by the solar absorptance (.alpha..sub.s) showing the absorption factor for absorbing the solar energy and the thermal emittance (.epsilon.) showing the radiation factor for emitting thermal energy. In order to maintain the temperature of an antenna within a pre-set range, .alpha..sub.s should be low and .epsilon. should be high.
An antenna of an artificial satellite is also exposed to an electron ray, gamma rays and ultraviolet rays, and the temperature thereof becomes so low as approximately to -(minus) 180.degree. C. when it is kept in the shade. Accordingly, the coating composition should not be deteriorated by radioactive or ultraviolet rays to have an increased solar absorptance, and cracking, peeling or any other disorders should not be caused in the coating within a temperature range of from -180.degree. C. to 100.degree. C. So it is also necessary that changes in .alpha..sub.s and .epsilon. be small.
H. A. Parazian has reported the solar absorption changes of the conventional thermal control coatings in his article, AIAA-84-0059, "Solar Absorption Changes of Thermal Control Coatings During Flight" in AIAA 22nd Aerospace Sciences Meeting, held by American Institute of Aeronautics and Astronautics on Jan. 9 to 12, 1984 at Reno, Nevada. In this report, he investigated the changes in solar absorptance (.alpha..sub.s) of thermal control coatings coated on a satellite which had flied for 5 years. His report discloses, for example, a white paint composed of a binder made of a silicone-alkyd resin added with titanium oxide. However, since this paint is applied approximately 100 .mu.m thick, a light weight coating of not more than 150 g/m.sup.2 cannot be formed by using the same. A further disadvantage is that the coating is easily deteriorated by UV irradiation to have an increased .alpha..sub.s, and for this reason it would pose problems when applied on a satellite of long life time. There is a demand for a white paint which forms a thin coating excellent in durability in the aerospace environment, as a large satellite of long life time is required in recent years.